US2534917A

US2534917A - Synchronized hoist control for dredge draglines

Info

Publication number: US2534917A
Application number: US742613A
Authority: US
Inventors: George E King
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1947-04-19
Filing date: 1947-04-19
Publication date: 1950-12-19
Anticipated expiration: 1967-12-19

Description

G. E. KING Dec. 19, 1950 SYNCHRONIZED HOIST CONTROL FOR DREDGE DRAGLINES Filed April 19, 1947 19/0 Current lNVENTOR Gear-9e E K "79.

WITNESSES:

ATTORNEY Patented Dec. 19, 1950 SYNCHRONIZED HOIST CONTROL FOR DREDGE DRAGLINES George E. King, Edgewood, Pa., assignor to West- 7 inghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 19, 1947, Serial No. 742,613

15 Claims.

This invention relates to positioning control apparatus and, more particularly, to apparatus for regulating the relative positions of the separate sections of a drag-pipe during raising and lowering operations with respect to a dredging ship on which the drag-pipe is mounted.

In certain types of dredging operations, the dredging ship is provided with a drag-pipe which is dragged over the bed of a body of water and through which the silt and muck to be dredged is drawn into the body of the dredging ship. The drag-pipe is pivotally connected to the ship with which the dredging operations are conducted and is constructed of two relatively mov-- able sections coupled together by a flexible coupling. When the drag-pipe is pivotally moved about its point of connection to the ship during raising and lowering operations, it is desirable that the relatively movable sections of the drag-pipe be maintained in predetermined relative axial positions with respect to each other. Specifically, this invention in one of its aspects deals with apparatus for raising and lowering a drag-pipe which is effective to maintain the relative positions of the drag-pipe sections during raising and lowering. In a broader sense, this invention deals with a control system for maintaining two objects in positional agreement with each other as they are moved from one position to another.

One of the principal objects of this invention is to provide apparatus for controlling the operation of drag-lines during raising and lowering operations of a drag-pipe which is effective to maintain the relative positions of sections of the drag-pipe with respect to each other during raising and lowering operations.

A further object of the invention is to provide a control system for maintaining a pair of motors or motor-driven elements in positional agreement with each other.

A further object of the invention is to provide, in a control system of the character referred to, a pair of rheostats which are adjustable to positions corresponding, respectively, to the movement of a pair of motors or motor-driven objects together with control apparatus responsive to the positional disagreement of the rheostats for regulating the operation of the motors in such manner to maintain the motors or objects driven thereby in positional agreement with each other.

A still further object of the invention is to provide a novel arrangement of an amplifying generator for regulating the operation of a pair of motors or objects driven thereby so as to maintain such motors or objects in positional agreement with each other. e

Other objects and advantages of the invention will become apparent from the following description.

In the drawing there is shown a preferred embodiment of the invention. In this showing:

Fig. 1 is a diagrammatic sketch illustrating the construction of a motor control system corresponding to the principles of this invention, and

Fig. 2 is an explanatory graph.

Referring to Fig. 1 of the drawing, the numeral l designates the stern of a dredge ship supported by a body of water 2. A drag-pipe 3 is pivotally connected at one end 4 to the ship for pivotal movement from a raised position, as illustrated, to a lowered position, in which the free end 5 of the drag-pipe will be engaged with the material to be dredged from the bed of the water 2 through the drag-pipe 3. The dragpipe 3 is formed of two sections 6 and 1 connected together by a flexible coupling 8. During raising and lowering movements of the dragpipe 3 relative to the ship i, it is desirable to maintain the drag-pipe sections 6 and I in axial alignment or at a predetermined angular position relative to each other.

To raise and lower the drag-pipe 3, a dragline 9 is connected thereto adjacent its free end 5, and a drag-line I0 is connected thereto adjacent the flexible coupling 8. The draglines 9 and I0, respectively, are operated by dragwinches H and I2. The drag-winch II is mechanically connected to a motor 23, and the dragwinch I2 is similarly connected to a motor I4. Reduction gearing (not shown) will be provided in actual practice for connecting the motors l3 and M to the winches H and I2 driven thereby. Since the drag-line 9 must travel through a greater distance than the drag-line HI due to the arcuate path of travel of the pointsof connection of the drag-lines 9 and It to the dragpipe 3 about different radii during raising and lowering operations, provision may be made in the gear reduction mechanism connecting the drag-winches to their driving motors for compensating for such difference in movement. As an alternative and preferable scheme for compensating for the different distances of travel of the points of connection, the drums or winches II and I2 may be built with different size diameters so that a given movement of each winch 3 will pay out or heave in a different length of drag-line.

The motors l3 and it have their terminals connected in parallelwith the terminals of a direct current generator 55 which is provided with a stabilizing series field it. A suitable motor (not shown) is provided for driving the generator l5 at a constant speed. Manually operable switches ll and it are provided in the connections of the motors l3 and M to the generator l5, in order that such motors may be operated at will independently of each other.

Field windings l9 and Eli are provided for controlling the operation of the motor I3 and similar field windings 2i and 22 are provided for controlling the operation of the motor M. The

windlugs

23 and 22 are of separately excited type and I are connected to a suitable source of direct-current potential, such as the direct-current buses 23, through manually adjustable rheostats 24 and 25. Adjustment of the rheostats 24 and 25 will be eiiective to vary the speed of operation of the motors it and i l.

The field windings iii and ill regulate the operation of the motors iii and it in a manner to be described and are connected in series with a regulating generator 2% having a series field winding 2'5 and an adjustable rheostat 28 connected in s with its armature circuit. The regulating ge :rator 2-:3 has its rotor mechanically connected to the rotor of the generator l5, as diagrammatically indicated by the broken line 29.

The operation of the generator i5 is controlled through a winding connected by an adjustable rheostat iii and double-pole double-throw reversing switch 32 to a suitable source of, direct-current, as diagrammatically illustrated by the battery The circuit to the winding 33 is completed through the manually operable switch E i and a normally closed relay switch 35. Operations the reversing switch 32 will reverse the flow of current through the field winding so to change the polarity of output from the generator l5 and thereby reverse the operation of the motors i3 and id. Starting and stopping of the system may be controlled by operation of the manually operable switch 3 which controls the energization of the winding 38, and thereby the output of the generator [5. In connection with the control features provided by the reversing switch 32 and the manually operable switches 34, ii and 53, it is to be understood that such controls are diagrammatic for the purposes of this description and that in actual practice the usual conventional controls for controlling the operation the generator iii and selective op eration of the motors l3 and M will be provided.

The output of the generator 26, which regulates the energization of the regulating field windings l9 and 22 for the motors it and M, is under the control of a field winding 353 which has its terminals connected in shunt with the movable elements a? and 3 1 of potentiometer-type rheostats 39 and it. Each of the rheostats 39 and 48 has one terminal of its resistance element connected to one of the buses by the lead d2. The manuall adjustable resistance ill connects the other resistance terminal of the rheostat 39 to the other of the buses 23 and the manually adjustable re sistance Z3 similarly connects the other resistance terminal of the rheostat All to the other of the buses 23. The resistances ll and .3 provide an angular adjusting feature of a nature to be referred to later. By connecting the rheostats in the manner described, the movable elements 3'! and 38, will be at the same potential when they occupy the same relative angular position with respect to the

resistance elements

39 and 40. With the movable elements 31 and 313 in the same rela tive angular positions, as indicated in the draw ing, the elements 31 and 38 will be at the same potential and there will be no current flow in the circuit to the control field winding 36 and such winding will be deenergized. However, when the elements 3'! and 38 are moved to different positions relative to each other, they will be at different potentials, and the winding 36 will be energized in a direction and an amount corresponding to the angular displacement of the elements 3'? and 38 with respect to each other. A relay coil (it is included in the circuit to the control field winding 36 for energizing a solenoid 45 to open the contact 535 and shut down the apparatus when the elements El and 38 move too far out of positional agreement with each other. The movable elements 3'! and 38 of the

rheostats

39 and 40 are mechanically connected, respectively, to the motors l3 and M, as schematically indicated by the

broken lines

46 and 41. In this manner adjustment of the rheostats 39 and ll! by movement of the movable elements 31 and 38 will be a measure of the angular movement of the motors i3 and ill and of the rotation of the drag-winches ii and Since the drag-winches II and 12 are connected to the dragpipe 3, such movement of the movable elements 31 and 33 will also be a measure of the movement of the free end 5 of the drag-pipe 3 and of the flexible coupling 8. Displacement of the rheostat elements 3'? and 38 with respect to each. other will thereby be an indication of relative movement between the dragpipe sections 5 and i, and such displacement is employed through the regulating generator 25 to control the operation of the cot-ore l3 and M in a manner to maintain the rotors of such motors in angular agreement with each other and thereby the drag-pipe sections 6 and l in axial alignment with each other.

Relative movement between the drag-pipe sections 6 and I out of axial alignment with each other during raising and lowering movements of the drag-pipe 3 is caused by the motors l3 and M operating at different speeds and moving out of positions in angular agreement with each other. This relative movement will cause movement of the rheostat elements 3i and 38 to positions out of angular agreement with each other to thereby energize the control field Winding 36 and vary the output of the regulating generator 26. in order that the varying output of the regulating generator 25 will be effective to regulate the operation of the motors l3 and M to bring such motors back into positions of angular agreement with each other and to thereby return the dragpipe sections 6 and I to positions in axial alignment with each other, the windings l9 and 2| are wound in reverse fashion so that a varia tion in the output of the regulating generator 25 will be effective. to cause one of the motors l3 or H to speed up and the other of such motors to slow down. The speed regulation of the motors l3 and M is continued until the appropriate parts are brought back into positions of agreement with each other.

The regulating generator 28 is an amplifying type of generator which is effective to amplify the change in excitation of the control winding 36, which change in excitation in a measure of the difference in angular positions of the movable rheostat elements 31 and 38. By amplifying the control values fed to the control field Winding 36 by the

rheostats

39 and 46, the motors l3 and I 4 and parts driven thereby will be maintained more closely in positions of angular agreement with each other. In order that the generator 25 will be effective to provide maximum am-, plification of the control values fed to the control winding 35, the resistor 28 is adjusted to a critical value, providing what is termed herein as instable operation of the regulating generator 25. What is meant by insta'ble operation will be best understood by referring to the explanator curve of Fig. 2 which shows the saturation curve X of a direct-current series generator having a series field winding, such as the series field winding 21. As is well known, stable operation of a series generator is possible only if the resistance of its armature circuit is less than that of a line R tangential to the saturation curve X, such as a resistance corresponding to the line Y. For a resistance corresponding to the line Y, the generator voltage will build up to the point of intersection of the line Y with the saturation curve X, such as the point Y or Y, and stable operation will be had at such points and other points along the saturation curve X outwardly from the points Y and Y". For a resistance greater than the line R tangential to the saturation curve X, such as a resistance corresponding to the line Z, the generator voltage cannot build up. For a resistance in the load circuit of a series generator corresponding to the line B, the generator may have a value equal to any of the ordinates along the line of tangency of the line R with the saturation curve X. The resistor 28 is adjusted to a critical value for the regulating generator 26 corresponding to the line B, so that the output of the generator 26 may be regulated between the points R and R" along its saturation curve. In this manner a very slight change in the field current of the generator 26, as by a varying control current in the field winding 36, will be effective to cause an amplified output voltage from the regulating generator 26. From the foregoing, it will be understood that when the generator is described as having instable operation herein and in the claims, there is meant a series generator of the self-excited type, having the resistance of its load circuit adjusted to a value at which it may be regulated substantially along the straight line portion of its saturation curve.

With the regulating generator 25 adjusted for instable operation in the manner described above, external field control will be provided by the control field winding 36 to hold its output stead at a given point along its saturation curve between the points R and R. In other words, a balance condition will be effected with the output of the regulating generator 26 at a steady value maintaining the motors l3 and 14' and parts driven thereby in positions of angular agreement with each other. In the event that such parts move out of positions in angular agreement with each other, the

rheostats

39 and 40 will function immediately through the regulating generator 25 to effect th proper regulation of the motors l3 and Id.

The foregoing description has proceeded on the assumption that the drag-pipe sections are to be maintained in axial alignment with each other. For this purpose the adjustable resistances are not essential since they are used only for the purpose of placing the resistance terminals of the

rheostats

39 and 40 at the same relative po-' tenti als. If it is desired that the sections 8 and I occupy an angular position relative to each other, then it is merely necessary to adjust one of the resistances ll or 43 according to the direction of angular inclination desired. Adjustment of one of such resistances will change the voltage drop along the resistance element of the appropriate rheostats 39 and 4B and place the movable elements 3! and 38 at difierent potentials. This will energize the field 36 to displace the motors i3 and M an amount to move the elements 31 and.

38 to positions at which their potentials are equal. After the system has reached a condition of balance with the driven elements occupying new positions out of agreement with each other an amount corresponding to the adjustment of one of the resistances ll or 43, the system will operate as described above to maintain the relative positions of the driven parts displaced from each other a predetermined amount. If desired, the resistances 4| and 4'3 may be gauged for simultaneous operation. Although the description has been applied specifically to the application of the system for maintaining the relative positions of drag-pipe sections, it will be understood from the foregoing that the system is equally applicable to the positioning of other apparatus where drive motors or objects driven thereby are to be maintained in positional agreement or in relative positions displaced from each other a predetermined amount.

Since numerous changes may b made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In dredging apparatus on a dredge ship the combination of, a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe comprising a dragline connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said drag-lines, respectively, being provided with a drag-winch and a motor for operating the same, control means for said motors operative to maintain the sections of said pipe in a selected angular position with respect to each other during raising and lowering operation of said pipe, and means for adjusting said control means to efiect unequal operation of said motors and thereby angularly displace said dragpipe sections relative to each other a selected amount, said control means being operable after operation of said adjusting means to maintain said sections angularly displaced said selected predetermined amount during subsequent raising and lowering operations of said drag-pipe.

' 2. In dredging apparatus on a dredge ship, the combination of, a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe compris.

ing a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said draglines, respectively, being provided with a dragwinch and a motor for operating the same. control means for correlating the operation of said motors to maintain said sections in a selected angular position with respect to each other during raising and lowering operations, a pair or" rheostats each movable in accordance with the movement with respect to said dredge ship of the points of connection of said drag-1ines with said drag-pipe, means operative upon movement of said rheostatse out of positional agreement with each other in response to movement of said sections out of said relative angular position to uperate said control means to return said sections to their selected angular position relative to each other, and means for adjusting the operation of said rheostats to effect a preselected angular displacement of said sections relative to each other, said control means being thereafter operable to maintain the preselected angularly displaced condition of said sections.

3. In a dredging apparatus on a dredge ship, the combination of, a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe comprising a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said dragline, respectively, being provided with a dragwinch and a motor for operating the same, control means for said motors comprising an individual control field winding for each of said motors, a regulating generator for energizing said wind ings, said windings being arranged so that when one of said windings operates to increase the excitation of one of said motors the other of said windings operates to decrease the excitation of the other of said motors, and means operative upon relative movement of said sections out of the selected angular position relative to each other in response to unequal operation of said motors during raising or lowering operations of said drag-pipe to vary the output of said generator to thereby operate said motors to return said pipe sections to said selected angular position relative to each other.

4. In a dredging apparatus on a dredge ship, the combination of, a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe comprising a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said draglines, respectively, being provided with a dragwinch and a motor for operating the same, control means for said motors comprising an individual control field winding for each of said motors, a regulating generator for energizing said windings, said windings being arranged so that when one of said windings operates to increase the excitation of one of said motors the other of said windings operates to decrease the excitation of the other .of said motors, a pair of rheostats responsive to the movements with respect to the dredge ship of the points of connection of said drag-line with said drag-line, respectively, and means responsive to movement of said rheostats out of a normal position relative to each other in response to angular movement of said sections relative to each other for varying the output of said generator to thereby operate said motors to return said sections to said selected relative angular position.

5. In a dredging apparatus on a dredge ship, the combination of a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe comprising a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said drag-lines, respectively, being provided with a drag-winch and a motor for operating the same, control means for said motors comprising an individual control field winding for each of said motors, a regulating generator for energizing said windings, said windings being arranged so that when one of said windings operates to increase the excitation of one of said motors the other of said windings operates to decrease the excitation of the other or" said motors, a pair of rheostats responsive to the movements with respect to the dredge ship of the points of connection of said draglines with said drag-pipe, respectively, a control circuit including a regulating field winding for said generator bridging said rheostats, said rheostats being operative upon movement out of positional agreement with each other in response to angular movement of said sections relative to each other during raising and lowering operations of said drag-pipe to supply a regulating potential to said regulating winding to vary the output of said generator and thereby operate said motors to return said pipe sections to their said selected relative angular position with respect to each other.

6. In a dredging apparatus on a dredge ship, the combination of a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularly relative to each other, means for raising and lowering said pipe comprising a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said drag-lines, respectively, being provided with a drag-winch and a motor for operating the same, control means for said motors comprising an individual control field winding for each of said motors, a regulating generator for energizing said windings, said windings being arranged so that when one of said windings operates to increase the excitation of one of said motors the other of said windings operates to decrease the excitation of the other of said motors, said regulating generator having an armature circuit including a series field and a resistance, the resistance of said circuit being selected to provide instable operation of said generator, a control field winding for said generator separate from said series field, and means operative upon movement of said sections out of their selected angular position relative to each other during a raising or lowering operation of said drag-pipe for varying'theen'ergization of said generator control 1 field winding to thereby vary the output of said generator and operate said motors to return said pipe sections to their selected angular position relative to each other.

7. In a dredging apparatus on a dredge ship, the combination of, a drag-pipe supported at one end by the dredge ship for pivotal movement with respect thereto, said drag-pipe being formed of two sections and having a flexible coupling connecting said sections to provide for movement of said sections angularlyv relative to each other, means for raising and lowering said pipe comprising a drag-line connected to said pipe adjacent its free end and a drag-line connected to said pipe adjacent said coupling, each of said drag-lines, respectively, being provided with a drag-winch and a motor for operating the same, control means for said motors comprising an individual control field winding for each of said motors, a regulating generator for energizing I said windings, said windings being arranged so that when one of said windings operates to increase the excitation of oneof said motors the f other of said windings operates to decrease the excitation of the other of said motors, a control field winding for said generator, said generator being provided with a series field winding and a resistance in its armature circuit, said resistance being adjusted to a critical value providing instable operation of said generator such 1 angular position relative to each other during a raising or lowering operation of said drag-pipe for varying the energi'zation of said generator control field winding to thereby vary the output 1 ,of. saidgenerator and operate said motors to return said pipe sections to their selected angular position relative to each other.

8. In positioning control apparatus, a pair of machines the respective positions of which are to be maintained in positionalagreement with each other, each of said machines being provided with a regulating field winding, said field windings being arranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field windings will be decreased, a regulating generator for energizing said field windings, said generator having a series field winding and a resistance in its armature circuit and a control field winding separate from said series field, said resistance being adjusted to a critical value providing instable operation of said generator such that a small variation in the energizatic-n of said control field winding will result in an amplified output of said generator, and means controlling the energization of said control field winding including a pair of rheostats respectively operable to positions corresponding to the positions of said machines, and circuit means for energizing said control field winding in accordance with the positional disagreement of said rheostats to vary the output of said generator and thereby the operation of said machines so as to maintain said machines in positional agreement with each other.

9. In positioning control apparatus, a pair of machines the respective positions of which are to be maintaiined in positional agreement with each other, each of said machines being provided with a regulating field winding, said field windings being arranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field control field winding to vary the output of said generator and thereby regulate the operation of said machines to restore their condition of positional agreement with each other.

10. In positioning control apparatus, a pairof machines the respective positions of which'are to be maintained in positional agreement with each other, each of said machines being provided with a regulating field winding, said field windings being arranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field windings will be decreased, a regulating generator for energizing said field windings, said regulating generator having an armature circuit including a series field and a resistance, the resistance of said circuit being selected to provide instable operation of said generator, a control field winding for said generator separate from said series field, and means operative upon movement of said machines out of positional agreement with each other for varying the energization of said control field winding to vary the output of said generator and thereby regulate the operation of said machines to restore their condition of positional agreement with each other.

11. In positioning control apparatus, a pair of machines the respective positions of which are to be maintained in positional agreement with each other, each of said machines being provided with a regulating field winding, said field windings being arranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field windings will be decreased, a regulating generator for energizing said field windings, a control field winding for said generator, and means operative upon movement of said machines out of positional agreement with each other for varying the energization of said control field winding to vary the output of said generator and thereby regulate the operation of said machines to restore their condition of positional agreement with each other.

12. In positioning control a paratus, a pair of machines the respective positions of which are to be maintained in positional agreement with each other, each of said machines being provided with a regulating field winding, said fiield windings being arranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field windings will be decreased, a regulating generator for energizing said field windings, a control field winding for said generator, and means controlling the energization of said control field winding including a pair of rheostats respectively operable to positions corresponding to the positions of said machines, and circuit'means for energizing said ,control field winding in accordance with the positional disagreement of said rheostats to vary the output of said generator and thereby the operation of said machinesso as to maintain said ariachines in positional agreement with each other.

13. In positioning control apparatus, a pair of machines the respective positions of which are to be maintained in positional agreement with .eachlother, each of said machines being provided with :a ;regulatingfie1d Winding, said field windings ;being arrranged so that when the excitation provided by one of said windings is increased the excitation provided by the other of said field windings will be decreased, a regulating generator :for energizing said -=field :windings, a control field winding :for said generator, and :means controlling the cnergiza-tion of said control field winding including a pair of rheostats respectively operable to positions corresponding to the positions of said machines, and

"circuit means 'for energizing said control field winding in accordance with the positional disagreement of said rheostats to varythe output of said generator and thereby the operation of said machines 50 as to maintain said machines in positional agreement with each other, and means for adjusting the operation of said rheostats to effect each other in response to movement of said imachines out of positional agreement with each other for operating said regulating means to return said machines to their normal condition in positional agreement with each other and an adjustable resistance ,.for varying the operation of at least one of said rheostats to thereby change the respective positions of said machines which are to the maintained in positional agreement with each other.

15,. In positioning control apparatus, a :pair of machines the respective positions of which are .to be maintained in positional agreement with each other, regulating means for correlating the operation cf said machines to maintain them in a normal condition in positional agreement with each other comprising a regulating generator having a variable output, a pair of :rhecstats movable in accordance with the positions of said machines respectively, and means operative upon movement of saidrheostats out of positional agreement with each other in response to :movement .of :said machines out of positional agreement for varying the output of said generator to thereby regulate the operation of said machines to restore their normal condition in positional agreement with each other.

GEORGE E. KING,

REFERENCES CITED The ltollowing references are of record in the file of this patent:

UNITED STATES PATENTS 709,509 France May '18, 1931